Non-visual imaging method based on space-based platform

Abstract

The application discloses a non-visual imaging method based on a space-based platform, and comprises the following steps: obtaining minimum laser energy; obtaining a maximum position of windowing, and obtaining minimum pulse period according to the maximum position of windowing; obtaining maximum sampling time; a laser emits laser light according to the minimum laser energy, the minimum pulse period and the maximum sampling time, samples data, and extracts first peak energy and second peak energy of the data; if a square root of the first peak energy is greater than a feasible signal-to-noise ratio of the first peak and a square root of the second peak energy is greater than a feasible signal-to-noise ratio of the second peak, a sampling start time and a sampling posture are predicted according to a first peak energy formula and a second peak energy formula; the laser emits laser light according to the sampling start time and the sampling posture, collects sampling data, and obtains a reconstructed voxel probability map according to the sampling data and a preset reconstruction operator. The application meets the imaging scene of real-time video stream in a larger range.

Description

Technical Field

[0001] This invention belongs to the field of non-line-of-sight imaging technology, and particularly relates to a non-line-of-sight imaging method based on a space-based platform. Background Technology

[0002] Non-line-of-sight (NLOS) imaging technology aims to solve the problem of imaging occluded targets in specific scenarios. Unlike traditional imaging systems that collect photon energy transmitted in free space within the field of view, NLOS imaging technology often uses active optics to achieve effective imaging of occluded targets.

[0003] From a technical principle perspective, non-line-of-sight (NLOS) imaging technologies can be categorized into active sensing methods based on lasers and mechanical waves, and passive sensing methods based on infrared radiation. Among these, the most promising solution employs precise measurement of photon event occurrence times, followed by a reconstruction algorithm built upon physical laws for efficient NLOS target inversion and reconstruction. Currently, ground-based and handheld NLOS imaging technologies are progressing towards practical application. Through optoelectronic system design and algorithm acceleration, real-time reconstruction of NLOS target video streams is becoming feasible.

[0004] Existing technologies focus on improving modular functionality and performance, primarily conducting research on principle verification based on ground-based platforms. However, there is currently no research on system-level solutions for spaceborne applications. This has the negative effect of limiting the detection range, restricting it to detection in a specific area and failing to meet the imaging requirements of real-time video streams over a wider area. Summary of the Invention

[0005] The technical problem solved by this invention is to overcome the shortcomings of the prior art and provide a non-line-of-sight imaging method based on a space-based platform, which is no longer limited to the detection of a certain area and meets the imaging scenarios of real-time video streams over a wider range.

[0006] The objective of this invention is achieved through the following technical solution: a non-line-of-sight imaging method based on a space-based platform, comprising: the space-based platform receiving a working command and tracking the target point to be explored; obtaining the minimum laser energy based on solar irradiance, non-line-of-sight target albedo, solar incidence angle, distance between the visible wall and the target, laser pulse width, non-line-of-sight target area, and feasible signal-to-noise ratio of the second peak value; obtaining the maximum windowing position based on the albedo of the visible wall, non-line-of-sight target albedo, pixel projection area on the ground, non-line-of-sight target area, feasible signal-to-noise ratio of the second peak value, laser pulse width, laser energy, solar irradiance, solar incidence angle, and the angle between the principal optical axis and the normal of the visible wall; obtaining the minimum pulse period based on the maximum windowing position; and obtaining the minimum pulse period based on the visible wall albedo, non-line-of-sight target albedo, pixel projection area on the ground, non-line-of-sight target area, feasible signal-to-noise ratio of the second peak value, laser pulse width, laser energy, solar irradiance, solar incidence angle, and the angle between the principal optical axis and the normal of the visible wall. The maximum sampling time is obtained by considering the Euclidean straight-line distance between the wall and the space-based platform, the maximum rotational angular velocity of the space-based platform, the relative ground velocity, and the stability. The laser emits a laser based on the minimum laser energy, the minimum pulse period, and the maximum sampling time, and samples the data. The first peak energy and the second peak energy of the data are extracted. If the square root of the first peak energy is greater than the feasible signal-to-noise ratio of the first peak energy and the square root of the second peak energy is greater than the feasible signal-to-noise ratio of the second peak energy, the sampling start time and sampling attitude are predicted based on the formulas for the first peak energy and the second peak energy. The laser emits a laser based on the sampling start time and sampling attitude, collects the sampling data, and obtains the reconstructed voxel probability map based on the sampling data and the preset reconstruction operator.

[0007] In the above-mentioned non-line-of-sight imaging method based on a space-based platform, the target point to be explored is the intersection of the main optical axis and the visible wall surface.

[0008] In the above-mentioned non-line-of-sight imaging method based on a space-based platform, the minimum laser energy is obtained by the following formula:

[0009]

[0010] in, For the minimum laser energy, E sun ρ is the solar irradiance. object For the albedo of non-visual targets, θ sun Let r be the angle of incidence of sunlight, r be the distance between the visible wall and the target, Δτ be the laser pulse width, and A be the angle of incidence of sunlight. object For the area of ​​the non-view target, SNR s2 The feasible signal-to-noise ratio for the second peak value.

[0011] In the above-mentioned non-line-of-sight imaging method based on a space-based platform, the maximum position of the window is obtained by the following formula:

[0012]

[0013] Where, r maxWhere ρ is the maximum position of the window opening, ρwall is the albedo of the visible wall surface, ρobject is the albedo of the non-view target, and A wall Let A be the projected area of ​​a pixel on the ground. object For the area of ​​the non-view target, SNR s2 The feasible signal-to-noise ratio for the second peak value, Δτ is the laser pulse width, and E Laser For laser energy, E sun θ represents solar irradiance. sun Let θ be the angle of incidence of sunlight. n2o The angle between the principal optical axis and the normal of the visible wall surface.

[0014] In the above-mentioned non-line-of-sight imaging method based on a space-based platform, the maximum sampling time is obtained by the following formula:

[0015]

[0016] Where N is the number of pulses, Δt is the pulse period, R is the Euclidean straight-line distance between the visible wall and the space-based platform, and ω max V is the maximum rotational angular velocity of the space-based platform. ground For relative ground velocity, Δ S For stability, A wall (m,n) represents the projected area of ​​pixel (m,n) on the ground, where m is the x-coordinate of the pixel and n is the y-coordinate of the pixel.

[0017] In the above-mentioned non-line-of-sight imaging method based on a space-based platform, the formula for the first peak energy is:

[0018]

[0019] Among them, E s1 The first peak energy is given by Υ, the proportionality coefficient is given by N, and the number of pulses is given by E. Laser For laser energy, A wall Let θ be the area of ​​the pixel projected onto the ground. n2o The angle between the principal optical axis and the normal to the visible wall, ρ wall Let α be the albedo of the visible wall, R be the Euclidean distance between the visible wall and the space-based platform, and α be the distance between the visible wall and the space-based platform. Atm This is the air attenuation coefficient.

[0020] In the above-mentioned non-line-of-sight imaging method based on a space-based platform, the formula for the second peak energy is:

[0021]

[0022] Among them, E s2 E is the second peak energy. s1 For the first peak energy, ρ object For non-line-of-sight targets, A objectdenoted as the area of ​​the non-visual target, and r as the distance between the visible wall and the target.

[0023] In the above-mentioned non-line-of-sight imaging method based on a space-based platform, the reconstructed voxel probability map is obtained by the following formula:

[0024] V(M,N,T)=A(m,n,M,N,T)*Sig(m,n,T);

[0025] Where V() is the reconstructed voxel probability map, A() is the reconstruction operator, Sig() is the sampled data, m is the x-coordinate of the pixel, n is the y-coordinate of the pixel, M is the horizontal index of the voxel on the visible wall, N is the vertical index of the voxel on the visible wall, and T is the time.

[0026] A non-line-of-sight imaging system based on a space-based platform includes: a first module for obtaining the minimum laser energy based on solar irradiance, non-line-of-sight target albedo, solar incidence angle, distance between the visible wall and the target, laser pulse width, non-line-of-sight target area, and feasible signal-to-noise ratio of the second peak value; a second module for obtaining the maximum windowing position based on the albedo of the visible wall, non-line-of-sight target albedo, pixel projection area on the ground, non-line-of-sight target area, feasible signal-to-noise ratio of the second peak value, laser pulse width, laser energy, solar irradiance, solar incidence angle, and the angle between the principal optical axis and the normal of the visible wall, and obtaining the minimum pulse period based on the maximum windowing position; a third module... The first module is used to obtain the maximum sampling time based on the Euclidean straight-line distance between the visible wall and the space-based platform, the maximum rotational angular velocity of the space-based platform, the relative ground velocity, and the stability. The second module is used to sample the data and extract the first peak energy and the second peak energy. The third module is used to predict the sampling start time and sampling attitude based on the formulas for the first peak energy and the second peak energy if the square root of the first peak energy is greater than the feasible signal-to-noise ratio of the first peak energy and the square root of the second peak energy is greater than the feasible signal-to-noise ratio of the second peak energy. The fourth module is used to collect the sampled data and obtain the reconstructed voxel probability map based on the sampled data and the preset reconstruction operator.

[0027] An electronic device includes: a memory for storing computer-readable instructions; and a processor for executing the computer-readable instructions to perform a non-line-of-sight imaging method based on a space-based platform.

[0028] Compared with the prior art, the present invention has the following advantages:

[0029] (1) This invention is no longer limited to the detection of a certain area, but meets the imaging scenarios of real-time video streams over a larger area;

[0030] (2) The present invention can perform feasibility assessment and rapid acquisition of signals from non-line-of-sight targets based on space-based platforms;

[0031] (3) The present invention can perform real-time data measurement of non-line-of-sight targets based on a space-based platform and reconstruct the video stream of the downlink voxel probability map. Attached Figure Description

[0032] Various other advantages and benefits will become apparent to those skilled in the art upon reading the following detailed description of preferred embodiments. The accompanying drawings are for illustrative purposes only and are not intended to limit the invention. Furthermore, the same reference numerals denote the same parts throughout the drawings. In the drawings:

[0033] Figure 1 This is a schematic diagram of a space-based non-line-of-sight imaging system provided in an embodiment of the present invention;

[0034] Figure 2 This is a flowchart of a non-line-of-sight imaging method based on a space-based platform provided in an embodiment of the present invention;

[0035] Figure 3 This is a schematic diagram of irradiation point conversion provided in an embodiment of the present invention. Detailed Implementation

[0036] Exemplary embodiments of the present disclosure will now be described in more detail with reference to the accompanying drawings. While exemplary embodiments of the present disclosure are shown in the drawings, it should be understood that the present disclosure may be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided to enable a more thorough understanding of the present disclosure and to fully convey the scope of the disclosure to those skilled in the art. It should be noted that, unless otherwise specified, the embodiments and features described herein can be combined with each other. The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0037] Figure 1 This is a schematic diagram of a space-based non-line-of-sight imaging system provided in an embodiment of the present invention. Figure 1 As shown, the space-based non-line-of-sight imaging system consists of eight subsystems: camera, laser, processing, integrated electrical system, power supply, control, data transmission, and telemetry and control. The camera subsystem includes an array detector and its circuitry; specifically, the array detector includes SPAD-type single-photon detectors. The flow of control signals, power, and data between the subsystems is as follows: Figure 1 As shown, the integrated power subsystem, as the control core, is connected to each subsystem by control signals, while the power supply subsystem, as the energy core, is connected to each subsystem by energy flow. The camera subsystem receives information from each pixel in parallel via an array, and after processing by the processing subsystem to generate the final non-line-of-sight target information, it is transmitted to the ground by the data transmission subsystem.

[0038] Space-based non-line-of-sight (NLOS) imaging technology, with its more flexible deployment and wider geographical reach, differs from traditional NLOS imaging technologies and possesses significant application potential. This embodiment proposes a space-based NLOS imaging method that leverages the unique orbital characteristics of spaceborne platforms and addresses the application requirements of online real-time data acquisition and reconstruction.

[0039] Figure 2 This is a flowchart of a non-line-of-sight imaging method based on a space-based platform provided in an embodiment of the present invention. For example... Figure 2 The aforementioned non-line-of-sight imaging method based on a space-based platform includes:

[0040] The space-based platform received the work order and began tracking and exploring the target point.

[0041] According to solar irradiance E sun Non-line-of-sight target albedo ρ object Sunlight incident angle θ sun Distance r between visible wall and target, laser pulse width Δτ, and area A of non-visual target. object Feasible signal-to-noise ratio (SNR) for the second peak s2 To obtain the minimum laser energy; based on the albedo ρ of the visible wall surface. wall Non-line-of-sight target albedo ρ object The projected area A of a pixel on the ground wall Non-visual target area A object Feasible signal-to-noise ratio (SNR) for the second peak s2 Laser pulse width Δτ, laser energy E Laser Solar irradiance E sun Sunlight incident angle θ sun and the angle θ between the principal optical axis and the normal of the visible wall. n2o The maximum opening position of the window is obtained, and the minimum pulse period is derived from this maximum opening position. The Euclidean distance R between the visible wall and the space-based platform, and the maximum angular velocity ω of the space-based platform are also considered. max Relative ground speed V ground and stability Δ S Obtain the maximum sampling time;

[0042] The laser emits laser light based on the minimum laser energy, minimum pulse period, and maximum sampling time, samples the data, and extracts the first peak energy and the second peak energy of the data.

[0043] If the square root of the first peak energy is greater than the feasible signal-to-noise ratio of the first peak and the square root of the second peak energy is greater than the feasible signal-to-noise ratio of the second peak, the formulas for the first peak energy and the second peak energy are obtained.

[0044] The sampling start time and sampling attitude are predicted based on the first peak energy formula and the second peak energy formula.

[0045] The laser emits laser light according to the sampling start time and sampling posture, collects sampling data, and obtains the reconstructed voxel probability map based on the sampling data and the preset reconstruction operator.

[0046] The target point to be explored is the intersection of the main optical axis and the visible wall surface.

[0047] The minimum laser energy is obtained using the following formula:

[0048]

[0049] in, For the minimum laser energy, E sun ρ is the solar irradiance. object For the albedo of non-visual targets, θ sun Let r be the angle of incidence of sunlight, r be the distance between the visible wall and the target, Δτ be the laser pulse width, and A be the angle of incidence of sunlight. object For the area of ​​the non-view target, SNR s2 The feasible signal-to-noise ratio for the second peak value.

[0050] The maximum opening position of the window is obtained using the following formula:

[0051]

[0052] Where, r max Where ρ is the maximum position of the window opening, ρwall is the albedo of the visible wall surface, ρobject is the albedo of the non-view target, and A wall Let A be the projected area of ​​a pixel on the ground. object For the area of ​​the non-view target, SNR s2 The feasible signal-to-noise ratio for the second peak value, Δτ is the laser pulse width, and E Laser For laser energy, E sun θ represents solar irradiance. sun Let θ be the angle of incidence of sunlight. n2o The angle between the principal optical axis and the normal of the visible wall surface.

[0053] The maximum sampling time is obtained using the following formula:

[0054]

[0055] Where N is the number of pulses, Δt is the pulse period, R is the Euclidean straight-line distance between the visible wall and the space-based platform, and ω max V is the maximum rotational angular velocity of the space-based platform. ground For relative ground velocity, Δ S For stability, A wall(m,n) represents the projected area of ​​pixel (m,n) on the ground, where m is the x-coordinate of the pixel and n is the y-coordinate of the pixel.

[0056] The formula for the first peak energy is:

[0057]

[0058] Among them, E s1 The first peak energy is given by Υ, the proportionality coefficient is given by N, and the number of pulses is given by E. Laser For laser energy, A wall Let θ be the area of ​​the pixel projected onto the ground. n2o The angle between the principal optical axis and the normal to the visible wall, ρ wall Let α be the albedo of the visible wall, R be the Euclidean distance between the visible wall and the space-based platform, and α be the distance between the visible wall and the space-based platform. Atm This is the air attenuation coefficient.

[0059] The formula for the second peak energy is:

[0060]

[0061] Among them, E s2 E is the second peak energy. s1 For the first peak energy, ρ object For non-line-of-sight targets, A object denoted as the area of ​​the non-visual target, and r as the distance between the visible wall and the target.

[0062] The reconstructed voxel probability map is obtained using the following formula:

[0063] V(M,N,T)=A(m,n,M,N,T)*Sig(m,n,T);

[0064] Where V() is the reconstructed voxel probability map, A() is the reconstruction operator, Sig() is the sampled data, m is the x-coordinate of the pixel, n is the y-coordinate of the pixel, M is the horizontal index of the voxel on the visible wall, N is the vertical index of the voxel on the visible wall, and T is the time.

[0065] The typical workflow of the time-saving and labor-saving methods involved in this process is as follows:

[0066] Step 1: Task begins. Upon receiving the work instruction, adjust the attitude of the space-based platform in real time to align the main optical axis with the point to be inspected. Typically, the point to be inspected is the intersection of the main optical axis and the visible wall surface.

[0067] Specifically, it follows the target point and maintains platform stability. It acquires the current attitude and trajectory information, where the attitude is represented as p(t) = [θ]. X (t),θ Y (t),θ ZThe position P(t) is given by the platform's own sensors, and the platform position P(t) = [α]. long (t),α lati [H(t), H(t)] are given by the navigation system to determine the laser projection size and pixel projection size. An evaluation function J(·) is introduced to evaluate the current attitude and orbit state's fulfillment of imaging requirements, calculating the fulfillment of each keypoint to control the platform's attitude. Keypoints include: laser illumination point and pixel projection point, with m and n representing the keypoint array indices. Based on partial derivatives... Generate control signals to perform attitude stabilization control on the platform.

[0068] Step 2: Feasibility Assessment. A series of laser beams with different parameters are emitted, and the echo signals are received to assess whether the laser and platform performance meet the requirements, thus determining mission feasibility. As the emitted laser energy increases, the presence and quantitative intensity and signal-to-noise ratio (SNR) of echoes from non-line-of-sight targets are acquired, and the laser parameters are dynamically adjusted. This continues until the SNR requirements for each detector are met. The visible wall illumination point range is then expanded, and the signal acquisition intensity of the array detectors is collected. The normal to the visible wall and the ground projection size and acquisition parameters of the available array are estimated. Finally, a comprehensive evaluation is conducted to determine whether the platform's stability and maneuverability meet the requirements, thus assessing mission feasibility. If not feasible, subsequent steps are not performed, and the mission is terminated prematurely.

[0069] Specifically, the visibility of non-line-of-sight targets is determined. Given specific laser parameters, attitude parameters, and acquisition parameters, the signal level of the echo from a non-line-of-sight target can be detected, described by the signal-to-noise ratio (SNR). The SNR level of the echo signal is improved by increasing the scanning laser emission energy and the number of laser pulses until satisfactory signal quality is obtained. If the echo signal quality of the non-line-of-sight target still fails to meet the requirements at the maximum number of laser pulses and maximum laser emission energy, the non-line-of-sight target cannot be detected, subsequent tasks are cancelled, and the situation is reported back. If the platform capabilities and SNR requirements are met, task planning for subsequent formal signal acquisition tasks begins.

[0070] Specifically, the laser and acquisition parameters are determined. For cases where the target is known or assumed to be outside the field of view, the minimum laser energy used during the measurement can be calculated using formula (1).

[0071] Adjusting laser parameters to scan its pulse period Δt and laser energy E Laser This allows for obtaining the optimal signal-to-noise ratio of the non-line-of-sight target signal and the shortest measurement time NΔt. The background noise E is measured during the NΔt time period by stopping laser emission. e .

[0072] Specifically, determine the maximum window position corresponding to the laser. Calculate the maximum window position using formula (2).

[0073]

[0074] Specifically, the sampling time is determined by the platform's maximum rotational angular velocity ω. max The platform maneuvers maintain the optical axis pointing towards the target point to keep the pointing of each pixel and illumination point stable, with a certain stability Δ S Point to each key point to ensure that the field of view does not exceed the projection area A within the sampling time. wall (m,n). Based on the relative ground velocity V during the measurement time period. ground (P(t)), the maximum sampling time that satisfies the platform's rotation capability and stability is determined by formula (3), and a feasibility judgment is made with the aforementioned minimum sampling time NΔt.

[0075]

[0076] If the task is feasible, perform the following calculations. Emit a series of divergence angle parameters towards the target point. By increasing the divergence angle, determine the distribution of available detector elements and calculate the projected area A of each pixel on the ground at different times. wall (p(t), P(t), m, n). Then, by fixing the divergence angle and measuring the echo time of each pixel, the visible wall normal is determined and denoted by n. From this, θ can be calculated. n2o (p(t),P(t)) corresponds to the angle between the optical axis and the normal to the visible plane at a specific moment. Atmospheric attenuation parameters and target / wall physical property parameters are determined based on formula (4) and measured data. Where Υ is a constant, and R is the Euclidean distance between the plane and the platform.

[0077]

[0078] Step 3: Task Planning. Based on the data measured in Step 2 and the orbital information, plan the instrument parameters necessary for acquiring data from non-line-of-sight targets, mainly including: acquisition start time, acquisition end time, laser energy, laser repetition rate, platform attitude at acquisition start, platform attitude at acquisition end, and gating time window. Simultaneously calculate the operators required for reconstruction and store them for later use.

[0079] Step 2, combined with the task planning algorithm, allows for the comprehensive calculation of the start / end times and attitudes that meet the acquisition conditions. During the planning process, the system initializes the laser's output energy E. Laser The system monitors the pulse interval Δt and the number of pulses N, continuously adjusts the equipment parameters based on the echo information, and dynamically maintains the feasibility of the task. If a special situation causes the task to fail, subsequent steps will not be executed, and the task will end prematurely.

[0080] For non-confocal optical systems, an equivalent transformation operator A(m,n,M,N,T) is used to generate the confocal configuration, accelerating the reconstruction process, relative to different reconstruction algorithms. For one reconstruction algorithm, the confocal scenario is equivalent, and a voxel cube indexed by the time signal dimension is constructed for each key point. Then, after the measurement signal arrives, the measurement cube is constructed using the index signal. By superimposing the data from multiple measurement points, the entire non-field-of-view imaging reconstruction process is completed.

[0081] Step 4: Execute the task and rebuild the downlink. Based on the planning results of Step 3, a certain number of laser pulses are emitted at the start of signal acquisition to complete the measurement. During the measurement process, the platform's attitude is adjusted to ensure the stability and quality of the received signal.

[0082] The obtained signal is processed by the reconstruction operator to obtain multiple frames of non-line-of-sight target voxel probability map data, which are then transmitted to the ground or stored. The mission is then successfully completed.

[0083] A typical calculation method is shown in formula (5), where V is the reconstructed voxel probability map and Sig is the signal collected at different key points.

[0084] V(M,N,T)=A(m,n,M,N,T)*Sig(m,n,T) (5)

[0085] In this embodiment, the atmospheric efficiency is initialized to 1, sunlight shines perpendicularly to the ground surface, and the laser angle is 10°. It is assumed that the non-line-of-sight target is a sphere with a diameter of 1m, 5m from the wall surface at the point of illumination, the wall surface reflectivity is 0.2, the non-line-of-sight target reflectivity is 0.5, and the wall surface area is 25m². 2 The area of ​​the non-visual target is 1.4m². 2 The instrument uses a laser with a center wavelength of 1550nm, a primary mirror aperture of 1.5m, a focal length of 0.8m, a 32×32 array SPAD detector, an instrument response of 500ps, a pixel size of 1μm, an orbital altitude of R≈H=300km, a ground speed of approximately 7.39km / s, a platform rotation capability of 0.8° / s, and a platform stability capability of 3×10 -4 If ° / s, then the corresponding maximum measurement time is approximately min(0.56s, 0.24s) = 0.24s.

[0086] The workflow is as follows:

[0087] Step 1: Upon receiving the mission command, adjust the optical axis to the target point (0°, 0°). Simulations show that the average access time for a single satellite meeting the observation conditions is approximately 11 seconds.

[0088] Step 2: With a single-frame signal-to-noise ratio (SNR) of 1, determine the minimum required laser pulse energy and the maximum windowing position according to formulas (1) and (2). The minimum laser energy corresponding to targets of 1-5m is 85nJ-24μJ. Scan the laser pulse energy at the highest repetition rate, simultaneously configure the windowing position of the acquisition system, and judge the echo SNR until the SNR is satisfied. s1 and SNR s2 Increase the acquisition time until the signal-to-noise ratio requirement is met or the energy is increased to the maximum. Then, based on the laser energy and repetition rate at this time, increase the laser divergence angle and repeat the above steps until all detectors receive signals that meet the requirements. Then the mission is feasible.

[0089] Step 3: If feasible, the measurement time ΔT for a single frame image is determined. Based on the measurement data and according to formula (4), the fitting calculation parameters include: A wall ρ wall α Atm A object ρ object ,r,θ n2o (t). Based on the equivalent confocal algorithm of the illumination point, the reconstruction operator is pre-calculated, for example... Figure 3 As shown. The 32×32 detector elements are uniformly distributed over a 25m area. 2 When the wall surface is visible and the laser irradiation point is in the center, it can be converted into an equivalent confocal sampling condition. The generated operator has an average absolute error of about 3mm for a 32×32×1024 voxel cube.

[0090] Step 4: Based on the orbital attitude prediction model and the mission planning algorithm, plan a measurement scheme that meets the expected signal-to-noise ratio. Key parameters included in the scheme are: measurement start time, emitted laser energy, number of pulses, windowing start point, windowing end point, platform attitude, and download start time. During the measurement process, the distributed computation of the measurement data by the reconstruction operator is simultaneously completed, and the reconstructed non-line-of-sight target data is downloaded to the ground as soon as possible.

[0091] This embodiment also provides a non-line-of-sight imaging system based on a space-based platform, the system comprising: a first module, used for determining the solar irradiance E based on the solar irradiance E sun Non-line-of-sight target albedo ρ object Sunlight incident angle θ sun Distance r between visible wall and target, laser pulse width Δτ, and area A of non-visual target. object Feasible signal-to-noise ratio (SNR) for the second peak s2 To obtain the minimum laser energy; the second module is used to determine the albedo ρ of the visible wall surface. wall Non-line-of-sight target albedo ρ object The projected area A of a pixel on the ground wall Non-visual target area Aobject Feasible signal-to-noise ratio (SNR) for the second peak s2 Laser pulse width Δτ, laser energy E Laser Solar irradiance E sun Sunlight incident angle θ sun and the angle θ between the principal optical axis and the normal of the visible wall. n2o The maximum window opening position is obtained, and the minimum pulse period is derived from this maximum window opening position; the third module is used to determine the Euclidean straight-line distance R between the visible wall and the space-based platform, and the maximum rotational angular velocity ω of the space-based platform. max Relative ground speed V ground and stability Δ S The system is divided into seven modules: a maximum sampling time, a second module for sampling data and extracting the first and second peak energies, a third module for obtaining the formulas for the first and second peak energies if the square root of the first peak energy is greater than the feasible signal-to-noise ratio of the first peak energy and the square root of the second peak energy is greater than the feasible signal-to-noise ratio of the second peak energy, a fourth module for predicting the sampling start time and sampling posture based on the formulas for the first and second peak energies, and a fifth module for collecting the sampled data and obtaining the reconstructed voxel probability map based on the sampled data and the preset reconstruction operator.

[0092] This embodiment also provides an electronic device, including: a memory for storing computer-readable instructions; and a processor for running the computer-readable instructions to execute a non-line-of-sight imaging method based on a space-based platform.

[0093] This embodiment employs real-time flexible detection of non-line-of-sight targets, focusing on solving the problem of information acquisition lag caused by delays in measurement and reconstruction during the full-link imaging process, and achieving efficient acquisition of non-line-of-sight information: ① For short-term measurement, a parallel scheme based on single laser point illumination and array detector reception is adopted, and each detector element only collects a small number of arriving photon events; ② For rapid reconstruction, the reconstruction algorithm is approximated as a translation-invariant operator for each receiving point, and an indexing method is used to reduce computational complexity, thereby completing real-time reconstruction of non-line-of-sight targets and forming a video stream for downlink.

[0094] This embodiment is no longer limited to the detection of a certain area, and can meet the imaging scenarios of real-time video streams over a larger range; this embodiment can perform feasibility assessment and rapid acquisition of signals from non-line-of-sight targets based on a space-based platform; this embodiment can perform real-time data measurement of non-line-of-sight targets based on a space-based platform and reconstruct the video stream of the downlink voxel probability map.

[0095] Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make possible changes and modifications to the technical solutions of the present invention by utilizing the methods and techniques disclosed above without departing from the spirit and scope of the present invention. Therefore, any simple modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solutions of the present invention shall fall within the protection scope of the technical solutions of the present invention.

Claims

1. A non-line-of-sight imaging method based on a space-based platform, characterized in that... include: The space-based platform received the work order and began tracking and exploring the target point. The minimum laser energy is obtained based on solar irradiance, non-line-of-sight target albedo, solar incidence angle, distance between the visible wall and the target, laser pulse width, non-line-of-sight target area, and feasible signal-to-noise ratio of the second peak value. The maximum windowing position is obtained based on the albedo of the visible wall, non-line-of-sight target albedo, pixel projection area on the ground, non-line-of-sight target area, feasible signal-to-noise ratio of the second peak value, laser pulse width, laser energy, solar irradiance, solar incidence angle, and the angle between the principal optical axis and the normal of the visible wall. The minimum pulse period is obtained based on the maximum windowing position. The maximum sampling time is obtained based on the Euclidean straight-line distance between the visible wall and the space-based platform, the maximum rotational angular velocity of the space-based platform, relative ground velocity, and stability. The laser emits laser light based on the minimum laser energy, minimum pulse period, and maximum sampling time, samples the data, and extracts the first peak energy and the second peak energy of the data. If the square root of the first peak energy is greater than the feasible signal-to-noise ratio of the first peak and the square root of the second peak energy is greater than the feasible signal-to-noise ratio of the second peak, the sampling start time and sampling posture are predicted according to the formulas for the first peak energy and the second peak energy. The laser emits lasers according to the sampling start time and sampling posture to collect sampling data. The reconstructed voxel probability map is obtained based on the sampling data and the preset reconstruction operator. The minimum laser energy is obtained using the following formula: ； in, For the minimum laser energy, Solar irradiance, Albedo of non-visual targets Let be the angle of incidence of sunlight, and r be the distance between the visible wall and the target. The laser pulse width, For the area of ​​the non-visual target, The feasible signal-to-noise ratio for the second peak value; The maximum opening position of the window is obtained using the following formula: ； in, This is the maximum opening position of the window. For the area of ​​the non-visual target, The feasible signal-to-noise ratio for the second peak value. The laser pulse width, For laser energy, Solar irradiance, The angle of incidence of sunlight. The angle between the principal optical axis and the normal of the visible wall surface; The formula for the first peak energy is: ； in, This is the proportionality coefficient. The number of pulses. For laser energy, The projected area of ​​a pixel on the ground. The angle between the principal optical axis and the normal of the visible wall surface. Let R be the albedo of the visible wall, and R be the Euclidean straight-line distance between the visible wall and the space-based platform. The air attenuation coefficient; The formula for the second peak energy is: ； in, The second peak energy, The first peak energy, Albedo of non-visual targets denoted as the area of ​​the non-visual target, and r as the distance between the visible wall and the target.

2. The non-line-of-sight imaging method based on a space-based platform according to claim 1, characterized in that: The target point to be explored is the intersection of the main optical axis and the visible wall surface.

3. The non-line-of-sight imaging method based on a space-based platform according to claim 1, characterized in that: The maximum sampling time is obtained using the following formula: ； in, The number of pulses. R is the pulse period, and R is the Euclidean distance between the visible wall and the space-based platform. This represents the maximum rotational angular velocity of the space-based platform. Relative ground speed, For stability, For pixels In the ground projection area, The x-coordinate of the pixel is The vertical coordinate of the pixel is denoted as y.

4. The non-line-of-sight imaging method based on a space-based platform according to claim 1, characterized in that: The reconstructed voxel probability map is obtained using the following formula: ； in, This is the reconstructed voxel probability map. To reconstruct the operator, For sampled data, The x-coordinate of the pixel is The ordinate of the pixel is For the horizontal index of voxels on the visible wall, For the vertical index of voxels on the visible wall, For a moment.

5. An electronic device, characterized in that, include: Memory: Used to store computer-readable instructions; as well as Processor: for executing the computer-readable instructions to perform the method as described in any one of claims 1 to 4.

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